This invention relates to nuclear reactor containment arrangements, and more particularly to permanent seal rings extending across an annular thermal expansion gap between a peripheral wall of a nuclear reactor vessel and a containment wall wherein the seal ring provides a water tight seal across the expansion gap allowing for lateral translation of the reactor vessel relative to the containment wall.
Nuclear reactor vessels are typically positioned within a cavity defined by a concrete containment wall that may also contain shielding material. The containment wall is generally cylindrical in shape, having an upper portion defining a refueling canal above the reactor vessel and a lower portion spaced apart from and surrounding the reactor vessel. The annular expansion gap between the peripheral wall of the reactor vessel and the containment wall allows for thermal expansion and lateral movement of the reactor vessel in relation to the containment wall. Generally, the refueling canal is maintained dry during normal reactor operations. However, during refueling the upper portion of the reactor vessel is raised to expose the reactor core for the exchange of fuel assemblies. During the refueling operation, it is advantageous to fill the refueling canal with water to provide additional shielding. It is generally not desirable to fill the entire space defined by the containment wall with water, but rather to only flood the upper portion defining the refueling canal. A water tight seal ring is therefore provided across the annular gap between the peripheral wall of the reactor vessel and the containment wall at the boundary between the refueling canal and the lower annular portion, or well, in which the vessel is positioned.
Typically, the reactor vessel has a horizontally extending flange and the containment wall has a horizontally extending ledge at about the same elevation at which the seal ring attaches. Although removable gasket type seal rings are known, the elastomeric gaskets used must be carefully installed during each refueling operation and are susceptible to thermal degradation and leakage. Furthermore, the gasket must be replaced during each refueling operation.
It is advantageous to provide a permanent seal ring to reduce the time required for the refueling operation. However, permanent seal rings need to allow for thermal expansion of the reactor vessel that reduces the gap between the peripheral wall of the reactor vessel and the containment wall, and also ideally provide for some vertical and lateral movement of the reactor vessel relative to the containment wall. In addition, the seal ring should be able to withstand heavy blows from objects, such as fuel assemblies, accidentally dropped during refueling. Thus, the seal ring must have (1) strength to retain the large volume of water used in the refueling operation; (2) flexibility to accommodate movement of the reactor vessel within the containment wall; and (3) structural integrity to resist damage from falling objects.
Prior art seal rings are discussed in U.S. Pat. No. 4,747,993 to Hankinson et al. and in U.S. Pat. No. 4,904,442 to Swidwa et al., the disclosures of which are herein incorporated by reference. Although those designs provide accommodation for radial and axial thermal expansion/contraction of the reactor vessel relative to the containment wall experienced during reactor operation, they fail to provide for lateral movement of the reactor vessel relative to the containment wall. Such movement of the reactor vessel, that may be encountered during operation of the reactor, can cause a loss of integrity of the seal ring.